Photocatalytic Oxidative Coupling of Methane to Ethane Using Water and Oxygen on Ag<sub>3</sub>PO<sub>4</sub>-ZnO
Yu-Xiong Wang, Yaoyu Zhang, Yue Liu, Zhongbiao Wu
Abstract
Photocatalytic oxidative coupling is an effective way of converting CH 4 to high-value-added multi-carbon chemicals under mild conditions, where the breaking of the C–H bond is the main rate-limiting step. In this paper, the Ag 3 PO 4 -ZnO heterostructure photocatalyst was synthesized for photocatalytic oxidative coupling of methane (OCM) to C 2 H 6 . In addition, an excellent C 2 H 6 yield (16.62 mmol g –1 h –1 ) and a remarkable apparent quantum yield (15.8% at 350 nm) at 49:1 CH 4 /Air and 20% RH are obtained, which is more than three times that of the state-of-the-art photocatalytic systems. Ag 3 PO 4 improves the adsorption and dissociation ability of O 2 and H 2 O, benefiting the formation of surface hydroxyl species. As a result, the C–H bond activation energy of CH 4 on ZnO was obviously reduced. Meanwhile, the improved separation of photogenerated carriers on the Ag 3 PO 4 -ZnO heterostructure also accelerates the OCM process. Moreover, Ag nanoparticles (NPs) derived from Ag 3 PO 4 reduction by photoelectrons promote the coupling of *CH 3, which can inhibit the overoxidation of CH 4 and increase C 2 H 6 selectivity. This research provides a guide for the design of catalyst and reaction systems in the photocatalytic OCM process.